Process for the manufacture of cellulose acetate film



Patented Nov. 24, 1931 UNITED STATES PATENT OFFICE ALBERT r. SULZEB, or RocnEsTER, NEW YoRK, ASSIGNOR To EASTMAN KODAK oom- PANY, or ROCHESTER, NEW Storm, A CORPORATION or NEW YORK PROCESS FOR THE MAN'UFACTURE 0F OELLULOSE ACETATE FILE NO Drawing.

This invention relates to the making of sheet material of a composition including a cellulose acetate. One object of this invention is the making of such a sheet thatwill have the quality of flatness to an unusual degree. I have discovered that this is particularly attained if the cellulose acetate has a high water resistance and I define this property by a criterion described herein.

Flatness of such sheet material is particularly desirable in large cut film, sensitized and used for photographic and X-ray purposes where buckling tends to result from the photographic baths. It is also desirable in cut sheets used for windows, or the like, as on intermediate lamination in reinforced glass where intimate fiat contact, free from bubbles and waves, is desirable; motion picture film and other purposes such as thin sheets for wrappin purposes.

It has ever been t e goal of photographic film manufacturers to produce a film, that could be cut into thin various cut film sizes, that would remain flat. The flatness of the erstwhile popular glass plates has been almost impossible of attainment. It is most essential that cut films, especially those in the larger sizes, remain flat under rigorous atmospheric conditions, as these out films are replacing to a large extent the glass plates formerly used for many photographic purposes, for example in aerial topographical mapping where flatness of the film in the focal plane of the photographic camera is a mathematical necessity. When roll film of large size is used for aerial work, various mechanical expedients can be employed to assist the film to lie flat. These are not so adaptable to large cut film and flatness must be inherent in the latter.

While flatness is of prime importance in the photographic field, it, of course, is likewise useful in other arts in which sheet material is extensively utilized. When used for Wrapping purposes, for example, the appearance of the wrapped article is greatly enhanced by wrappings which remain flat and the keeping qualities of such articles are increased considerably if the wrapping tis- Application filed April 8, 1929. Serial No. 353,649.

Other expedients have been resorted to but I they all greatly increase the expense of producing the film. I have found, on the other hand, that flat films can be manufactured.

without many of the unnecessar operations heretofore employed and by usin cellulose acetate as the sole cellulosic material used.

Cellulose acetate soluble in chloroform, as produced by the usual tpretreating and acetylating methods or or example by the proce% described in U. S. Patent 1,683,347, H. Le B. Gray et al., Sept. 4, 1928, is hydrolyzed either by merely an addition of acetic acid and water or by an addition of acetic acid, water and a mineral acid to the products of acetylation, or by the addition of an aqueous mineral acid mixture to the chloroform soluble cellulose acetate separated from the acetylation reaction products. Any of the usual hydrolyzing baths, however, are suitable.

I have found that if the hydrolysis is stopped when approximately or more of a sample of the cellulose acetate removed from the bath precipitates in a mixture of 40% water and 60% acetone by volume, the resulting cellulose acetate has heretofore unattainable qualities and, particularly when stirring with a rubber stopper fitted with a shaft for the stirrer.) To this dope is added slowly from a pipette and with thorough stirring, 150 cc. of a mixture consisting of 2 parts of distilled water and 1 part acetone by volume. Care should be taken to keep the solvents and mixtures at 20 C. wherever volumes are being measured.

At the end of the addition of the acetonewater mixture, a mixture is obtained containing 40% water by volume (neglecting contraction) in which is suspended the precipitated acetate. This is allowed to stand for 12 hours at 20 C. 25 cc. of the clearest portion (supernatent solution) are removed with a pipette. At the end of this time precipitation has reached equilibrium and proceeds no further, and during the same time settling of the precipitate occurs. This 25 cc. is centrifuged in sto-ppered bottles at high speed until the liquid is perfectly clear. Exactly 5 cc. of the clear liquid are removed with a pipette and evaporated to dryness on a tared watch glass. IfW is the weight of the residue in grams the precipitation value which equals the per cent acetate precipitated,

=100-W X -Xl00 T have found that film produced from a hydrolyzed cellulose acetate that gives a precipitation value in the above test of approximately or better has a high-water resistance value and a flatness that is exceptional. It is, therefore, but necessary so to control the hydrolysis by suitable hydrolyzing baths that the cellulose acetate is accurately and consistently deacetylated to the prescribed precipitation value, in order to produce a material having these advantages. The method of so controlling this hydrolysis that a cellulose acetate having these values may be obtained is given in the pending application of Carl J. Malm, Serial No. 325,597 filed Dec. 12, 1928.

The precipitation value of 90% or more may be obtained by any of the usual hydrolyzing methods. I prefer, however, to use either of the following methods which I call the acid final or water final process of deacetylation. In the acid final type of hydrolysis, mineral acids (i. e. hydrochloric or phosphoric acids) are added with acetic acid and water to the so-called first stage cellulose acetate dope: that is, the cellulose acetate solution attained at the end of the acetylating step, usually a solution of a completely acetylated cellulose triacetate. The hydrolysis requries from 30 to 50 hours at a temperature of to F. It is somewhat difficult at all times to regulate the exact time at which the deacetylation should be stopped to give a precipitation value, as described above, of 90%; at a lower temperature, however, of say 70 F. the time treatment is increased to from 5 to 10 days which results in better control.

Of the two more preferable hydrolyzing processes I prefer, however, to use the water final method which I will now describe. This is carried out by the use of acetic acid and water Without the necessity of adding any catalysts other than those already found in the first stage cellulose acetate solution. At a temperature of 70 F. this hydrolysis will require, to give approximately a 90% precipitation value, 20 to 25 days; at a temperature of 90 to 100 F. the time may be reduced to from 8 to 12 days. It is obvious that the reaction rate in any of these long time methods is such that after determining the degree of precipitation, by removing a sample from the whole batch, the hydrolysis can be readily stopped before the optimum hydrolysis end point has been overstepped.

The cellulose acetates produced by the long time hydrolysis methods say over 5 days have a much higher viscosity than those produced by the shorter methods. The flexibility of the resulting films are also somewhat better in the longer period methods. For cut sheets or film purposes, however, flexibility is not of great importance, and the shorter methods are, therefore, somewhat preferable from the economical and equipment standpoints.

The acetate is used in any typical composition such as those given in the Patents 1,532,819, J. H. Haste, April 17, 1925; 1,641,- 411, S. J. Carroll, Sept. 6, 1927; and 1,309,- 980. H. T. Clarke, July 15, 1919, and the sheet of film is formed and coated with sensitive emulsion in the usual way.

Having thus described my invention what I claim as new and desire to secure by Letters Patent is 1. A sheet material having the property of flatness in an unusual degree and having as the principal ingredients thereof hydrolyzed cellulose acetate having a precipitation value of at least 90% in a solution consisting of 40% water and 60% acetone at 20 C. and a plasticizer for the cellulose acetate.

2. A photographic flexible cut sheet film having the properties of satisfactory flexibility and transparency and having to an unusual degree the properties of flatness and low water permeability and having as the principal ingredients thereof hydrolyzed cellulose acetate having a precipitation value of at least 90% in a solution consisting of 40% water and 60% acetone at 20 C. and a plasticizer for the cellulose acetate.

3. A flexible motion picture film having the properties of satisfactory flexibility and transparency and having to an unusual degree the properties of flatness and low water permeability and having as the principal ingredients thereof hydrolyzed cellulose aceprincipal ingredients hydrolyzed cellulose tate having a precipitation value of at least 90% in a Solution consisting of 40% water and 60% acetone at 20 C(and a plasticizer for the cellulose acetate.

4. A sheet material having an unusual resistance to moisture and comprising as its 

